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Sink or Swim: The Best Under Sink Water Heaters of 2021 – Reviews and Buying Guide

Hot water in our homes is one of life’s great luxuries - a modern wonder that’s easy to take for granted. From washing vegetables in the kitchen to lathering our hands in soap, warm water makes life easier.

But what happens when you turn on the faucet and get left out in the cold?

Or you’re just waiting for the boiler to kick in - wasting cold water down the drain?

Especially during winters, an icy blast of water is the last thing we need from the faucet. I suffer from Raunaud’s syndrome, and if my hands get chilled from cold tap water, it can take all afternoon to warm up again.

There are many reasons why your hot taps might be letting you down. Big houses can suffer from cold plumbing when the boiler is just too far from distant bathrooms. You could have brushed your teeth by the time the hot water reaches you!

Or maybe you simply don’t have a boiler, in the garage, greenhouse or outhouse. But wouldn’t a little warm water be nice to help out when you’re washing the car?

Fortunately, we’ve got just the thing. Under sink water heaters are easy to install and surprisingly affordable.

From great glugging tanks to streamlined tankless water heaters, these babies come in all shapes and sizes. Stealthy designs seamlessly blend into modern bathroom aesthetics, and big, ol’ industrial tanks stand out loud and proud.

We’ll take a deep dive into the world of under sink water heaters, checking out the best of the best. And then explore everything you need to know about under sink water heaters.

To paraphrase Sebatian, that jolly crab from Disney classic The Little Mermaid:

“Down where it’s wetter, it’s so much better, under the sink.”

The Best Under Sink Water Heaters of 2021

Hot water is an essential in modern homes and waiting for your water to warm up is a waste of energy as well as time. Here are the top rated under sink water heaters of 2021 to give you an instant hot water hit.

1. Bosch Electric Mini-Tank Water Heater - Best Choice For A Bigger Capacity

Bosch’s mini-tank water heater comes in 2.5, 4, and 7-gallon capacities, but we’ll focus on the 4-galloner as a compromise on size and capacity.

Bosch Electric Mini-Tank Water Heater

Pros

  • 4-gallon capacity for additional use
  • CFC-free foam
  • Extended power cable

Cons

  • No digital display
  • Longer waiting time for water over 90°F

The tank is well built - a solid plastic chassis houses the water tank, which is glass-lined making it extra durable. It’s insulated with CFC (chlorofluorocarbon)-free foam, and Bosch’s choice to eliminate chlorofluorocarbon demonstrates their green credentials. If you’re motivated to purchase a water heater based on a green streak, this is an added bonus.

The 4-gallon model is built for either floor- or wall-mounting and includes brackets to enable you to place the tank wherever is most appropriate. Mounting the tank on the wall in your under sink cabinets is a great way to maximize space in your kitchen or laundry room. 

With a simple toolkit, you’ll be able to install the tank without calling in the professionals. It’s mains powered and comes with an extended (36”) power cord, giving you further flexibility in fitting.

A tank front dial lets you choose the water temperature, running from min to max, through a handily labeled ‘ideal’ setting. However, an absence of a digital display means that you’re always guessing the temperature.

And when your 4 gallons is up, you’ll be waiting for water to reheat. For water flowing at 90°F, this will take under 30 mins but if you like your water superheated it’s a longer wait.

Bottom Line

4-gallon capacity gives you hot water at your fingertips, but if max out the capacity you’ll be waiting for a reheat.


2. Stiebel Eltron 233219 - Best For Quick Reheating

For second sinks or homes with less of a demand for hot water, smaller tanks are a great choice. The Stiebel Eltron’s 2.5-gallon capacity gives you instant hot water without taking up space.

Stiebel Eltron 233219

Pros

  • 6-year warranty
  • Energy efficient
  • Stylish design
  • T/P safety valve is professionally installed

Cons

  • Top-facing dial can be hard to reach

The stylish, flat-backed water tank is built for easy wall-mounting. Its premium white plastic chassis features a clean and minimalistic design, with just the Stiebel logo on the front. By placing the control dial on top, Stiebel have created a sleek water heater, but it also limits you in installation - you need to leave space above the unit to reach the dial.

The internal steel tank itself is glass-lined, meaning it’s a durable product but with a six-year warranty you have added reassurance about the Eltron’s quality. It’s also insulated, keeping water warmer for longer and creating an energy-efficient under sink water heater.

Installation is easy and Stiebel has included everything you need, minus the common tools. Brackets and screws allow for wall mounting and it can be plumbed in without requiring professional input.

Once installed, you’re good to go. Thanks to the smaller capacity it has a reheat time of just under 20 minutes. However, 2.5 gallons will last just a minute at common faucet flow rates - barely enough time to do the dishes.

Bottom Line

A bijou unit with limited capacity makes it perfect for small jobs in small spaces.


3. Camplux ME25 Mini Tank Electric Water Heater - Best Tank On A Budget

Camplux’s ME25 tank is a compact size, making it easy to squeeze in anywhere you need hot water in an instant.

Camplux ME25

Pros

  • Freeze protection setting
  • Super length 43” cord
  • Super easy to use

Cons

  • Warranty void if self-installed

It’s a classic white water tank, well-insulated to save energy. The tank is built of steel but glass-lined for added durability.

When it comes to installation, the 43” power cord exceeds what other manufacturers include as standard. With an extra foot of reach, you have even more flexibility around where to place your water heater.

Installation can be done at home by anyone with a handy streak - but be warned: the fine print reveals that self-installation will void the warranty of this product. But it might not be a bad idea to call in the professionals, as the safety T/P valve isn’t inbuilt and requires assemblage. Doing-it-yourself might entail some risks.

Once installed it’s easy to use. A front-facing dial limits water temperature - ranging from 60-140°F. It lacks the digital display that contemporary products sometimes include, but Camplux have helpfully identified 125°F on the sliding scale so you’re not just guessing between ‘min’ and ‘max’,

2.5 gallons won’t last forever, so you might be waiting for water to reheat if you leave the faucet flowing. The recovery rate at 90°F is 6.8GPH (gallons per hour) meaning it’ll take just over 20 minutes for water to return to that temperature. Of course, if you’re using the 125°F setting, it’s going to be closer to 30 so plan ahead.

Bottom Line

A compact unit with plenty of safety features. You’ll be splashing out on pro installation to preserve the warranty, but thanks to the low price tag you can afford it.


4. EcoTouch Tankless Water Heater Electric - Best Tankless Heater On A Budget

Tankless water heaters are fantastic space savers and can provide a continuous supply of hot water from your faucet. EcoTouch combines a stylish design and energy efficiency.

Tankless Water Heater Electric 240V

Pros

  • Tankless design
  • Digital touch panel and display
  • Chic, black design

Cons

  • Limited to 116°F for continuous flow
  • Professional installation is recommended

This slim-lined water heater is just 11" x 7.5" x 2.35" - the dimensions of a cereal box and can be mounted 360° in any space available.

It’s built for durability, featuring a thermal water chamber kept separate from the electronics, and the chic black design screams of modernity. All metal components are contained within the unit, and the external screen feels solid to the touch. This is a relief as flimsy touchscreens are a bane of modern technology.

EcoTouch recommend professional installation of the unit - but it comes with everything needed, from brackets to cables and it is compatible with common ½” piping. An experienced handyman can do the job with no specialty plumbing skills required.

Water is heated fast and effectively, up to 116°F in a continuous flow - however, for temperatures beyond this limit the flow rate will be affected. Even at 116°F, the flow rate is limited to around 1.5 GPM, slightly below your average faucet.

The unit stands out for its energy efficiency thanks to an auto-adjustment of power based on the required temperature and flow rate. If you turn the faucet on full, the EcoTouch will increase the power to keep up.

Lastly, the LCD display is fantastic for targeting precise water temperature. The gauge is accurate within +/- just 1°.

Bottom Line

A stylish and modern water heater that will fit just about anywhere.


5. Eccotemp EM-2.5 - Best Compact Water Tank

Ecotemp’s 2.5 gallon under sink water heater won’t be winning any design award. Compared to many minimalistic and stylish water heaters, it features a more basic aesthetic of blue and white, and the light-up power and heat indicators seem unnecessary.

Eccotemp EM-2.5

Pros

  • 99% energy efficient
  • Compact design
  • Easy-installation

Cons

  • Unaesthetic design
  • At least 20 minutes to recover hot water after use

It is, however, a particularly compact unit, and at 15” x 13.5” its almost square design will fit better into under-sink cabinets and other spaces than many competitors. If you’re looking for a space-saver, you’ve found it.

It’s an easy-install unit that doesn’t require plumbing expertise - hosing attaches to input cold water and output the hot, which can then be connected to your faucet. You’ll need to source these ½” pipes separately, but otherwise all connectors and brackets are included.

Temperature is controlled by a front-facing dial but simply runs from “off” to “max”, meaning there’s some guesswork involved in the output. It offers an output of 150 psi  - more than enough pressure for standard homes and shouldn’t limit the flow rate of even the most powerful faucets.

However, with just 2.5-gallon capacity, running out of hot water is on the cards at such a high psi. The recovery rate of 20-45 minutes, depending on the required temperature, is a little slow - but more energy efficient.

And the Ecotemp does indeed boast exceptional energy efficiency - over 99%. That’s going to save you a few bucks on your heating bill.

Bottom Line

No style points but a highly compact and energy-efficient water heater.


6. EcoSmart ECO 11 - Best For Continuous Flow

A highly efficient tankless water heater with a lifetime warranty - this is a premium under sink water heater but it comes with a premium price tag. Let’s take a closer look.

EcoSmart ECO 11

Pros

  • Lifetime warranty
  • 99.8% efficiency
  • Provide water heated to 105°F in a continuous flow at 1.5GPM

Cons

  • Cluttered design - best to be tucked away in a cabinet
  • Professional installation is a must

EcoSmart’s ECO 11 tankless heater is a streamlined water heater designed to blend seamlessly into bathroom and kitchen design. In terms of appearance, it’s far from a minimalist design -  actually, with a digital display, swivel dial on the front, and EcoSmart branding it’s almost cluttered.

It may not be the best-looking product, but EcoSmart have gone to lengths to build a powerful and efficient water heater. The tankless design allows this to be a slim and chic unit that can fit easily around any sink in your home.

However, with great power comes great responsibility. Because this unit requires 125 amp power, it isn’t immediately compatible with the power supply in most homes. A qualified electrician will need to install and wire the unit - otherwise, it could become a fire hazard in your home.

Once installed, however, you’ll have power and hot water to spare. The ECO 11 can provide a continuous flow of hot water, and running at 99.8% efficiency it can save your energy bill too.

The Eco 11 provides an adequate flow rate alongside its heating capacity - guaranteeing 1.5GPM when heating water by 60°F. That means, for example, that if your water is starting out at 45°F, the ECO 11 can provide water heated to 105°F in a continuous flow at 1.5GPM.

Bottom Line

A lifetime warranty makes the ECO 11 a safe buy - but to put safety first you’ll need professional installation for this powerful unit.


7. Thermoflow UT10 - Best Value for Money

Thermoflow’s 2.5 gallon under sink water heater is a good value product with easy installation and solid build quality including a stainless steel, low-maintenance tank.

Thermoflow UT10

Pros

  • Good value for money
  • Safety features
  • Super-heated settings

Cons

  • Short power cord
  • No option for wall mounting

The design is reminiscent of traditional boilers, giving it an industrial feel. However, it won’t look out of place amongst your other kitchen appliances. A tapered top gives you easy access to the settings dial.

Unlike many competitors’ products, however, Thermoflow’s water heater cannot be wall-mounted, but it fits snugly on the floor in under sink cabinets. The other thing to watch out for is the shorter power cord - at just 30”, you’ll need power close by.

These factors are certainly limiting where you can install the unit, but if you have the space and a power source, installation is an easy job. Simply attach the water inflow and outflow and plug it into any outlet.

Thermoflow’s heater stands out thanks to some added safety features, including an anti-freeze mode for when you’re not using the unit. This is great for colder climates where frozen pipes can damage your plumbing over the winter. It also has a max temperature of 167°F - hot stuff!

The 2.5-gallon tank is slow to reheat if you run out of hot water, so if your hot water needs are extensive Thermoflow could leave you hanging. For hand washing and tooth-brushing, however, it’s a powerful product.

Bottom Line

The combination of a low price tag and high top-end temperatures make this an appealing under sink water heater.


The Buyer’s Guide To Under Sink Water Heaters

From scrubbing dirty dishes to getting those teeth clean, you don’t want to be let down by your water heater.

Choosing the best water heater for your home and your family can be a complex challenge, but we’ve assembled everything you need to know so you can make a choice that doesn’t leave you feeling lukewarm about your purchase.

When To Buy An Under Sink Water Heater

Some people say that it’s opposable thumbs that separate us from the animal kingdom, but personally, I think it’s having hot water on-demand in our homes.

And whilst modern homes are fitted with boilers, it can be advantageous to install specialty under sink water heaters in particular locations. Having hot water on demand is a modern luxury to make the most of.

For Hot Water In The Outhouse

We can’t always rely on hot water being plumbed in outside our homes. Having hot water coming steaming out of the faucet in the shed or garage can make those daily chores that much easier. From washing the car to cleaning up muddy pets, installing an under sink water heater can bring hot water to your outhouses.

When Your Boiler Can’t Keep Up

Even indoors, we often find our hot water system can’t keep up with the demands we place on it. It can be a painstaking wait for the boiler to heat up when the hot water faucet turns on, and often we waste gallons of water pouring from the tap in the process.

And if you live in a larger home, bathrooms at the extreme ends of the house are often so distant from the boiler that it feels like the hot water never makes it there. If you’re washing your hands for 30 seconds you can be left in the cold. Water heaters are an affordable solution, putting instant hot water in every room.

Pursuing A Greener Home

Energy efficiency is more important than ever as we face up to the challenges of climate change. Finding ways to reduce your energy bill saves a few dollars every month, and can also have a big impact on your environmental footprint.

Boilers are energy inefficient because they leave water to cool down in the pipes, but under sink water heaters only heat water you’re going to use. Well-insulated tanks mean that when water is heated it stays hot, and tankless heaters are even more efficient, heating water right before you use it and not a drop more.

Choosing Your Heater: Tank Heater vs Tankless

Besides a wide range of added features, there are two main ways in which under sink water heaters can vary. They either come with a tank - typically 2.5 - 7 gallon capacity, or they’re tankless and superheat water as it passes through a medium within the heater.

Tankless Water Heaters

Tankless water heaters typically command a higher price and are the more technologically advanced product. Often accompanied by digital displays and touch screens, they look at home in any modern kitchen or bathroom.

And because they don’t require a spacious tank, they’re chic and streamlined - usually taking up less space than a cereal box. Wall-mounted versions can be easily located anywhere in the home.

Tankless heaters also tend to be slightly more energy-saving than their tanked counterparts, using up to 33% more energy-efficient (1). That’s because they’re not storing any hot water - no matter how insulated a tank water heater is, there’s always some loss of heat. Tankless water heaters are red hot - and green!

Tank Water Heaters

Traditional tanked water heaters come in a range of sizes, but to squeeze them in below your sink you’ll likely prefer the compact 2.5 - 4 gallon options. If you only need small amounts of hot water on occasion, for example, to wash your hands in the bathroom, then just a couple of gallons of hot water is always adequate.

However, if you have the hot water faucet running, even four gallons can be used up in just a couple of minutes. The reheat time is therefore vital on tanked options and can range from a 20-minute wait to over an hour.

Tanked water heaters are usually easy to install and competitively priced - but running out of water is a real risk.

A Sad Lunch: The Cold Water Sandwich

Possibly the worst-sounding lunch in the world, a cold water sandwich isn’t actually soggy bread - but it’s just as disappointing. A cold water sandwich occurs when a tankless water heater ejects a small amount of cold water, still trapped in the system from previous use. Intermittent cold water is a risk from tankless heaters - so installing a hot water tank inline can give you the best of both worlds.

What To Look For When Buying An Under Sink Heater

Whether you're looking for a streamlined tankless under sink heater or a big daddy tank of hot water, there’s a lot to consider. Let’s take a look at the main things to consider when it comes to under sink heaters.

1. Size And Space

Under sink heaters come in a range of shapes and sizes, from slim ‘n’ sassy tankless heaters to big-capacity tanks. Before you start shopping for your under sink heater, assess the space in which you’re going to install it.

Wall-mounted heaters are space savers because, no matter the bulk, you maximize storage space below the heater itself. There’s also an aesthetic decision to make - small, tankless heaters have less of a design effect on your bathroom look and can sometimes blend seamlessly into the existing design.

2. Reheating Power

Tankless heaters can guarantee a continuous flow of hot water, but heaters keeping hot water in tanks can run out. In fact, a 2.5-gallon tank is likely to run out in under 60 seconds if you have high-powered faucets, so the reheating power of a tank is important.

Most heaters can regain a decent amount of heat in under 20 minutes, but if you like your water seriously hot, you may need a higher-powered heater to cut the time down.

3. Flow Rate

Flow rate is as important for faucets as it is for showerheads - we’ve all experienced disappointment in a dribble from the faucet, and at home we've often invested in powerful faucets to maximize flow. Don’t let your water heater slow you down.

Tank heaters rarely impact your faucet flow rate as the water is already heated and just waiting to be pumped through the pipes. With tankless versions, however, you’ll need to ensure they have the power to meet your flow expectations. 1.5GPM (gallons per minute) is a good benchmark for your under sink heater to meet.

4. Energy Efficiency

Reducing your energy consumption at home saves you money, and limits your impact on the environment. There are strong green incentives to invest in under sink heaters, so you might as well look for the most energy-efficient options. Heaters can range from 90-99.8% efficiency and are often energy rated on a scale from A to F.

Generally, tankless heaters are slightly more energy efficient. If you’re going green they’re a good option.

5. Voltage

Because under sink heaters are powerful devices, you need to make sure your electrical outlets can handle the heat. In the United States, the standard voltage for electrical outlets is 120V and is compatible with most under sink heaters. However, some modern, supercharged tankless heaters might require an adaptor.

6. Safety Features

Whilst you want hot water in the sink, you don’t want to find yourself getting into hot water for your troubles! Safety features such as a thermostat that switches the heater off if temperatures rise and freeze protection which prevents the heater from damage in a cold snap are worth the investment.

Most headers will have a T/P valve - standing for temperature/pressure. This should be professionally installed if it doesn’t come integrated into the unit to make sure your heater isn’t a hazard.

7. Installation

An appealing feature in many under sink heaters is the ease of install. Plumb in the cold water inflow and connect the outflow to your faucets, and then all you need to do is plug into mains power to have the warm water flowing.

However, some models are a little more complicated and either require plumbing experience to set up the T/P valve correctly or an electrician to ensure that the system is compatible with your home power supply. If you’re ever in any doubt, it’s time to call in the professionals.

What’s more, whilst some heaters are DIY-ready, to do so might void the warranty. This is frustratingly only found in the small print, so while a 5-year warrant might look good on paper, it’ll come at the price of professional installation.

8. Warranty

A word on warranty. No matter how much research you do, something can always go wrong from a factory fault to an unhappy accident. A warranty keeps you covered in an unfortunate eventuality. Whilst a year or two may be standard, some brands offer extended warranties of up to five or six years - and even lifetime warranties are available in some cases.

Final Thoughts...

From uber-chic tankless water heaters to big-capacity units, hopefully you’ve discovered that there’s an under sink water heater to fit into every kitchen, bathroom, or garage going.

And when you’re measuring them up, you need to think of everything from voltage to volume.

Never again find yourself asking if it’s worth washing your hands, or if you can suffer the chill of ice-cold water when you’re brushing your teeth. Instant hot water can be gushing out of your faucet at every sink in your home.

Efficient water heating saves you money on your energy bill, and reduces your water waste footprint. It’s a win-win for your purse and the planet.

So what are you waiting for? The perfect under sink water heater is out there, all you need to do is choose.


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